Field of the Invention
The present invention relates to a wireless relay device, a wireless communication system, and a wireless communication method.
Priority is claimed on Japanese Patent Application No. 2015-168224, filed on Aug. 27, 2015, the content of which is incorporated herein by reference.
Description of Related Art
All patents, patent applications, patent publications, scientific articles, and the like, which will hereinafter be cited or identified in the present application, will hereby be incorporated by reference in their entirety in order to describe more fully the state of the art to which the present invention pertains.
Conventionally, a distributed control system (DCS) has been constructed in plants or factories, and a highly automated operation has been realized. This distributed control system is a system in which a field device (measurement device or an operating device) and a control device that performs control of the field device are connected via communication means. Some communication systems that are a basis of such a distributed control system perform wired communication. In recent years, a wireless communication system that performs wireless communication conforming to Industrial wireless communication standard such as ISA100.11a or WirelessHART (registered trademark) has been realized.
In such a wireless communication system, it is necessary to ensure security. Accordingly, various items of data communicated over a wireless network are often encrypted using an encryption technology. For example, in a wireless communication system conforming to ISA100.11a described above, encryption is performed using an encryption key distributed from a management device that performs management of the wireless network to each field device. Since the encryption keys that are distributed to the respective field devices differ from each other, high security is ensured.
Shuji Yamamoto et al., “World's First Wireless Field Instruments Based on ISA100.11a”, Yokogawa Technical Report, Vol. 53, No. 2, 2010 (hereinafter referred to as Non-Patent Document 1) discloses an overview of a wireless communication system conforming to ISA100.11a described above. Further, Non-Patent Document 1 discloses a gateway in which a gateway function, a system management function (system manager), a security management function (security manager), and the like are integrated. In this gateway, distribution and updating of a security key (encryption key) are performed by the security management function.
Incidentally, in the above-described wireless communication system disclosed in Non-Patent Document 1, encryption keys for encrypting and decrypting data communicated over a wireless network are provided in a field device and a gateway. Therefore, various types of data transmitted from the field device are encrypted, transmitted to the gateway, decrypted, and centrally managed for each field device at a high-level device located at a high level of the gateway. However, such a management causes the following problems during an actual operation of the plant.
(1) Degradation of Efficiency of Plant Operation
If information obtained from a field device is managed for each field device, a high-level device generates alarm even when an abnormal field device does not directly influence on an operation of the plant. If the alarm is generated, for example, the plant stops until safety is confirmed by an operator. Accordingly, there is a problem in which efficiency of the operation of the plant is degraded. In an extreme example, in a large-scale wireless network (for example, a wireless network to which more than million wireless fields or the like are connected), a situation occurs in which the plant stops until the operator confirms content of the alarm and takes appropriate measures if the number of field devices in an abnormal state is 1.
(2) Increase in Burden of Operator
In a case in which alarms are generated from the high-level device, it is necessary for the operator of the plant to appropriately decide a degree of influence of the alarms on the operation of the plant and cope with the alarms, for each of the generated alarms. Therefore, it may be considered that the number of types of alarms and a frequency of generation of alarms also increase as a scale of the wireless network built in the plant increases. Accordingly, there is a problem in that a burden of the operator increases.
(3) Degradation of Efficiency of Device Maintenance Work
Since information transmitted from a field device to a high-level device includes information indicating a status of the field device, efficiency of work in the field is considered to be able to be improved if a worker performing conservation and maintenance work in the field can obtain information transmitted from the field device to the high-level device in the field. However, since various pieces of information transmitted from the field devices are encrypted, transmitted to the wireless network, and centrally managed in the high-level device, the worker in the field cannot utilize the information. Accordingly, there is a problem in that efficiency of device maintenance work is greatly degraded.